PROJECT SUMMARY Arsenic contamination of food and drinking water is a serious global health issue in the U.S. and worldwide. Arsenical skin lesions are a common and early sign of arsenic toxicity, but exposure to arsenic is also associated with risk for various types of cancer, cardiovascular disease, non-malignant respiratory disease, and shortened life span. A major focus of epidemiological research on arsenic exposure has been understanding genetic susceptibility to arsenic toxicity. Genetic studies have discovered roles for both inherited variation (e.g., AS3MT variants) as well as dynamic features of the genome (i.e., telomere length) in susceptibility to arsenic toxicity and response to exposure. Additional research is needed to fully understand these gene-environment relationships. The last decade of research on genetic susceptibility to disease in humans has clearly demonstrated that large studies with genome-wide measurement are highly likely to deliver discoveries that are re-producible. Thus, we propose creating a large genomic data resource in the context of an epidemiological study of arsenic exposure in rural Bangladesh. We will use this resource to identify the features of the human genome that reflect susceptibility or response to arsenic exposure. Our first goal is to extend our ongoing work on the genetics of arsenic metabolism efficiency (AME) and GxE (gene-by- environment interaction) to identify inherited variants that influence arsenic metabolism or arsenic toxicity. Under this goal, we will investigate the biological mechanisms of arsenic-related variants and evaluate the utility genetic information for exposure reduction. Achieving this goal will entail activities such as genome-wide association and heritability studies of AME and arsenical skin lesion risk, genome-wide searches for GxE, estimating the effects of SNPs on arsenic-related health outcomes, and evaluating the impact of returning genetic results to participants on exposure-related behaviors. Our second goal is to extend or our work on arsenic and telomere length to identify additional dynamic features of the genome that reflect biological response to arsenic or susceptibility to arsenic toxicity. Achieving this goal will entail testing numerous genomic features for association with arsenic exposure and arsenical skin lesion status, including somatic chromosomal losses and point mutations, DNA methylation, epigenetic aging, and mitochondrial DNA mutation and copy number. If successful, this project will provide novel biomarkers of susceptibility and toxicity as well as biomarkers of the biological effects of arsenic exposure. The biomarkers identified will provide information useful for (1) identifying subgroups of highly susceptible individuals, (2) understanding biological mechanisms underlying susceptibility and toxicity, and (3) motivating susceptible individuals to reduce their exposure. Furthermore, we will continue developing technologies for targeted measurement of copy number variable regions for large scale epidemiological and environmental health research. This work has the potential to have transformative impact not only on knowledge, but also on both global and local environmental health.